1. Field of the Invention
The present invention relates to an ultrasonic inspection method and to an ultrasonic inspection apparatus for inspecting metal or the like. The invention more particularly relates to an ultrasonic inspection method and to an ultrasonic inspection apparatus for inspecting a welded part for joining a structure (tube or vessel) partially or entirely having a cylindrical shape and another structure along a circumferential direction or along an axial direction or a direction in which a weld line extends with respect to the structure having the cylindrical shape.
2. Description of the Related Art
A method, such as an ultrasonic inspection method for inspection using an ultrasonic wave has been generally used as a nondestructive inspection method for inspecting a solid object such as metal. The following three inspection methods are known as ultrasonic inspection methods for inspecting a welded part (provided in a reactor pressure vessel) for joining a structure (tube or vessel) partially or entirely having a cylindrical shape and another structure along a circumferential direction or axial direction (direction of a welding line) of the structure having the cylindrical shape.
As the first method, an ultrasonic probe is placed on an inner surface of a penetration (a stub weld of a control rod drive mechanism attached to a lower head of a reactor pressure vessel) of the reactor pressure vessel to inspect the penetration through an immersion method in which water is injected in the penetration (refer to, for example, JP-A-7-244033).
As the second method, an ultrasonic probe is placed in a penetration (a stub weld of a control rod drive mechanism) of the bottom of a reactor pressure vessel, i.e., is placed on the inner side of the reactor pressure vessel to inspect the penetration (stub weld) (refer to, for example, JP-A-2005-300224).
As the third method, an ultrasonic probe is placed on the outer side of a reactor pressure vessel to inspect a welded part for joining the reactor pressure vessel and a structure provided in the reactor pressure vessel (refer to, for example, Non-Patent Document 1: AUTOMATED UT EXAMINATION OF BWR H8 & H9 CORE SHROUD WELDS USING PHASED ARRAY TECHNIQUES (Hector Diaz, Steven J. Todd, IHI Southwest Technologies, Inc.).